We investigated some enzymatic properties of the alkaline protease purified from ordinary carp muscle. The optimal pH of the enzyme for the hydrolysis of casein was found to be 8.0. The maximal activity of the enzyme was found at 65°C on 40 min incubation and the activity was not detected on incubation at temperatures under 55°C. The enzyme was stable at temperatures lower than 60°C for 10min, and also at pH values higher than 4.5 for 20hr at 3°C. The enzyme was activated by sulfhydryl compounds and was inhibited by sulfhydryl reagents such as K3, NEM and pCMB. The enzyme was inactivated by heavy metal ions, SDS, urea and NBS, but not by DFP. The enzyme inhibition by pCMB was reversed by the addition of excess 2-mercaptoethanol. The enzyme hydrolyzed casein and hemoglobin, but did not hydrolyze CBZ-Glu-Tyr, B-Arg amide, Gly-Phe amide and acid denatured hemoglobin, which were specific substrates for cathepsins A, B, C and D respectively. The hydrolysis of casein by this enzyme was inhibited by high concentrations of sodium chloride. Actomyosin was also considerably hydrolyzed by this enzyme in 0.12M sodium chloride, pH 8.4, but hardly hydrolyzed in 0.5M sodium chloride, pH 6.6, which is a condition similar to that used in the production of Kamaboko.